Study On The Morphology Of Local Scour Hole Around Bridge Pier During Ice Period And Discharge During The Break-Up Period

The safety of bridge engineering has always been the focus of research.Considering the safety of bridge piers during ice period,the research is carried out from the perspectives of local scour and ice flood during ice period.The research results can provide reference for engineering safety construction in cold area.The research on local scour around piers is of great significance in the bridge engineering.A large amount of ice cover occur frequently in northern rivers during the winter.The presence of ice cover has an effect on the local scour around bridge piers.In order to study the morphology of local scour hole around bridge pier under ice cover,a set of experiments were conducted in straight test flume under the condition of clean water scour.The sediment movement and variation around the cylindrical pier under ice cover were studied experimentally under different velocity,water depth,pier diameter and particle size.The results indicate that compared with open flow conditions,the existence of ice cover induces larger maximum scour depth and scour area,which leads to larger scour volume.Similar to the open flow conditions,the maximum scour depth and scour area under ice cover show an upward trend with the increase of the flow velocity,the increase of the pier diameter.Based on the regression analysis of the test data,a dimensionless calculation formula of the maximum scour depth,scour area and scour volume around bridge piers under open flow and ice-covered conditions is established,and compared with the research results of other scholars,which can provide certain reference for engineering practice.When the frozen river thaws during the break-up period,ice regime and water regime change drastically.Ice flood has a great influence on the hydraulic structures,it is difficult to forecast and the accuracy of forecast is low.Muskingum method and its derivation method are suitable for the discharge routing under open flow condition,but how to reflect the characteristics of flood in the ice flood season needs further study.Taking the Inner Mongolia reach of the Yellow River as an example,the discharge routing is carried out by analogy with the river channel with tributaries.Considering the propagation time of discharge,channel-storage increment is added into the calculation,and the modified Muskingum method is adopted to calculate the ice peak discharge during the break-up period.The results show that this method can well predict the discharge routing in ice flood season during the break-up period.According to the characteristics of ice flood,the type of flood is distinguished,and the cause of sudden change of discharge in ice flood season is revealed,which can provide a reference for the ice flood forecast during ice period.